Brentford have played good vs all the big clubs this season. Beat Arsenal drew 3-3 with Liverpool battered the phuck out of Chelsea in the first fixture. And made it very awkward for Citeh over their 2 games. And the United game at Brentford was close till the last 10-15 mins or so.
So Brentford beating up Chelsea shouldn't be that much of surprise going off their form this season.
4-1 at stanford bridge is a huge surprise